Avian Predation on Olive Ridley (Lepidochelys olivacea) Sea Turtle Eggs and Hatchlings: Avian Opportunities, Turtle Avoidance, and Human Protection

This study investigated avian predation on Olive Ridley (Lepidochelys olivacea) sea turtle eggs and hatchlings at the Ostional (Costa Rica) arribada beach. Our objectives were to identify avian predators and describe their behavior, examine avian foraging opportunities for obtaining eggs and hatchlings, describe different foraging opportunities, and to examine differences in the time hatchlings were exposed on the sand surface to avian predators as a function of time of day, sand temperature, number of hatchlings emerging at one time, and position in the emergence order (early, middle, or late). The timing of nesting and hatchling emergence, length of the incubation period, and heavy rains provided birds with foraging opportunities. Timing is critical because: 1) females nest in every month, but hatchlings require 45-65 days to hatch, thus nesting females dig up nests from previous nestings, 2) heavy rains increase stream flow, causing bank erosion, exposing nests to avian predators, 3) strong tides expose nests to avian predators, 4) hatchlings emerging in the early morning are visible to birds, and 5) length of time for hatchlings to emerge from the nest and reach the water varies among clutches. Black Vultures (Coragyps atratus), Wood Storks (Mycteria americana), and Great-tailed Grackles (Quiscalus mexicanus) accounted for most of the avian predation. Vultures foraged by searching for hatchlings on the surface, for eggs or hatchlings exposed by dogs or people, for clusters of birds around emerging hatchlings, and for opportunities to pirate eggs or hatchlings from other birds. Olive Ridleys avoid predation by predator swamping, nocturnal nesting, and nocturnal emergence of young. Humans decreased predation on hatchlings by removing debris that impedes hatchling movement to the sea, and by keeping predatory birds off the beach during the main early morning hatchling emergence period.